In this case, you still have the option of working with them to help them migrate to gamma@2, if the cost of maintaining gamma@1 is indeed too high and would negatively impact you in serving other customers. This was the original premise, wasn't it - upgrading all your dependants when you upgrade your library? That's still an option. The point is - you have more choices. And you can also help customers one by one - you don't have to do it all at once

I will agree though, restricting choices helps when the company is finding difficulty in aligning incentives through communication. But you do give up a lot for it - including ability to move fast and avoid stagnation.